The present disclosure generally relates to image conversion devices, and more particularly, to image conversion devices for generating synchronized horizontal synchronization signals and vertical synchronization signals.
As the technology evolves, various types of display devices are available on the market. Different display devices may have different specifications for image display. Sometimes, users may also want to watch the image in a format different from the format of the source image data. The source image data, therefore, may need to be converted to the appropriate format in order to be correctly displayed on the display device. Image conversion devices are used to convert the source image data to the appropriate format to be compatible with the specification of the display device, so that the converted image data may be displayed on the display device correctly. The image mentioned hereinafter may comprise pictures, videos, animations, and/or other visually acceptable material.
For example, when the source image frames of the resolution H1×V1 are displayed at a frequency of F Hz (i.e., in 1/F seconds), it means every source image frame has V1 scanlines and every scanline has H1 pixels. The image frames along with the corresponding vertical synchronization signals and horizontal synchronization signals are provided to the display device. The display device may update the image frames according to the vertical synchronization signals and update the scanlines according to the horizontal synchronization signals. Therefore, when generating the vertical synchronization signals and the horizontal synchronization signals, the horizontal blanking interval between the horizontal synchronization signals and the vertical blanking interval between the vertical synchronization signals should be configured to be compatible with the specification of the display device. For example, when the period of the pixel clock is Tclkp1 seconds, the period of the horizontal synchronization signals is (H1+a1)×Tclkp1 second. The H1×Tclkp1 seconds are used to transmit the data of the H1 pixels of a scanline in the source image frame and the a1×Tclkp1 seconds are used as the horizontal blanking interval. The period of the vertical synchronization signals equals (V1+b1) times the period of the horizontal synchronization signals, i.e., (V1+b1)×(H1+a1)×Tclkp1 seconds. The V1×(H1+a1)×Tclkp1 seconds are used to transmit the data of the V1 scanlines and the horizontal blanking intervals. The b1×(H1+a1)×Tclkp1 seconds are used as the vertical blanking interval.
When the source image frames of the resolution H1×V1 are to be displayed on a display device of the resolution H2×V2, the image conversion device needs to convert the source image frames of the resolution H1×V1 into the image frames of the resolution H2×V2. Furthermore, the image conversion device needs to provide the horizontal synchronization signals and vertical synchronization signals compatible with the specification of the display device. For example, when the period of the pixel clock supported by the display device is Tclkp2 seconds, the period of the horizontal synchronization signals of the converted image frame is (H2+a2)×Tclkp2. The H2×Tclkp2 seconds are used to transmit the data of the H2 pixels of a scanline to the display device and the a2×Tclkp2 seconds are used as the horizontal blanking interval. The period of the vertical synchronization signals of the converted image frames equals (V2+b2) times the period of the horizontal synchronization signals, i.e., (V2+b2)×(H2+a2)×Tclkp2 seconds. The V2×(H2+a2)×Tclkp2 seconds are used to transmit the data of the V2 scanlines to the display device and the horizontal blanking intervals. The b2×(H2+a2)×Tclkp2 seconds are used as the vertical blanking interval. Moreover, (V2+b2)×(H2+a2)×Tclkp2 seconds should equal to 1/F seconds so that the converted images frames may be synchronized with the source image frames.
In some applications, the source image frames are to be displayed on the display device of the resolution H1×V1, but the horizontal blanking interval and/or the vertical blanking interval need to be converted. For example, when the period of the pixel clock of the display device is Tclkp3 seconds, the image conversion device needs to provide the horizontal synchronization signals with the period of (H1+a3)×Tclkp3 seconds. The H1×Tclkp1 seconds are used to transmit the data of the H1 pixels of a scanline to the display device and the a3×Tclkp3 seconds are used as the horizontal blanking interval. The period of the vertical synchronization signals equals (V1+b3) times the period of the horizontal synchronization signals, i.e., (V1+b3)×(H1+a3)×Tclkp3 seconds. The V1×(H1+a3)×Tclkp3 seconds are used to transmit the data of the V1 scanlines to the display device and the horizontal blanking intervals. The b3×(H1+a3)×Tclkp3 seconds are used as the vertical blanking interval. Moreover, (V1+b3)×(H1+a3)×Tclkp3 seconds should equal to 1/F seconds so that the converted images frames may be synchronized with the source image frames.
When the horizontal synchronization signals and the vertical synchronization signals of the converted image frame are not synchronized, the data of the pixels of the last scanline in an image frame may not be completely displayed and abnormal images may be shown on the display device, e.g., freeze frames and lost frames. For example, when the start time of the vertical synchronization signals is different from the start time of the horizontal synchronization signals, or when the period of the vertical synchronization signals is not an integer multiple of the period of the horizontal synchronization signals, the horizontal synchronization signals and the vertical synchronization signals are not synchronized. Some image conversion devices try to solve the synchronization problem by adjusting the period of the pixel clock and the horizontal synchronization signals according to the format of the image frames to be displayed, e.g., the resolution, the horizontal blanking interval, the vertical blanking interval, and the display frequency. In the above example, the period of the pixel clock may be configured as 1/[(H2+a2)×(V2+b2)×F] seconds and the period of the horizontal synchronization signals may be configured as 1/[(V2+b2)×F] seconds so that the converted image frames may be displayed on the display device at F Hz. Complicated circuits and algorithms, however, are required to generate the appropriate period of the pixel clock and the horizontal synchronization signals for different resolutions. Besides, some display devices may not support the converted period of the pixel clock and the horizontal synchronization signals, and therefore may not output correct image frames. A simplified conversion device for resolving the compatibility problems is therefore needed.